1. The Field of the Invention
The present invention relates to composite materials and methods for making such materials, and in particular, to solid solutions of chemical components which are not appreciably miscible under equilibrium conditions. The present invention further relates to methods for modifying the surface structure of solid materials.
2. The Prior Art
In the preparation of chemical solutions, whether in the gaseous, liquid, or solid state, the mutual solubility or miscibility of the chemical components which are to form the solution is extremely important. Two chemicals which are relatively immiscible (and thus relatively insoluble) with respect to each other can generally not form a homogeneous solution having the desirable proportions of each component which would be needed to provide the chemical benefits of each component.
Often, it is desirable to form solid solutions of different chemical components. (As used herein, the term "solid solution" refers to a solution in which one or more chemical components (whether normally solid, liquid, or gas at room temperature) are dispersed throughout a solid host component or medium.) If the solid host medium and the chemical components which are desired to be dispersed therein are found to be immiscible using known techniques, such solid solutions have heretofore been impossible to form. Thus, there exists a large number of desirable yet heretofore merely hypothetical solid solutions which have not been prepared because of the immiscibility of the particular chemical components with respect to the solid host medium when conventional techniques have been used.
The utility of such "hypothetical" solid solutions would be enormous. For example, many compounds exist which are unstable in air, have bad odors, are toxic, are highly reactive or corrosive, are flammable, or are explosive in bulk. It would be extremely useful to isolate such compounds in a solid host medium which is relatively inert with respect to these compounds so as to form a solid solution; in such a solid solution, these compounds would be preserved in isolation for later use. Such isolation in the solid host medium would serve, for example, to increase the stability of these compounds upon exposure to air, to mask their bad odors, to control their toxicity, to prevent their premature or corrosive reaction with other substances or with themselves, to control their flammability, or to prevent their explosion.
Very little has been done in the prior art to develop methods whereby normally immiscible components may be combined to form a solid solution. One method used in the prior art to create unusual solid solutions involves inert gas matrices. Frozen inert gas matrices have been used to isolate various chemical species within a solid matrix so as to allow for study of the isolated species and/or its response to different stimuli. The formation of inert gas matrices is accomplished by codepositing the species to be isolated and the inert gas (which acts as the solid host medium) onto a cold wall under vacuum.
A typical procedure for forming an inert gas matrix is as follows: One or more chemical species to be isolated (e.g., a metal) is vaporized and introduced at a cold wall concurrently with an excess amount of an inert gas (typically argon). The cold wall is maintained at a temperature well below the freezing point of the inert gas (typically about 4-20K), so that the inert gas will exist in a solid state. Thus, upon codeposition of the species to be isolated with an excess of the inert gas onto the cold wall, a solid matrix is formed wherein the isolated species is dispersed throughout the solid argon. Typically, the species to be isolated is deposited with the inert gas onto the cold wall in a molar ratio of at least about 100:1 (inert gas:isolated species) to well above 1000:1.
In addition to argon, other host media have occasionally been used in such low temperature matrices, including xenon (Xe), nitrogen (N.sub.2), methane (CH.sub.4), sulfur hexafluoride (SF.sub.6), carbon monoxide (CO), and pentane (C.sub.5 H.sub.12). A substantial drawback of these prior art low temperature matrices if the fact that these matrices can only exist at temperatures where the host medium remains in a solid state; this means that for most of the widely-used matrices, the temperature is maintained below about 50K. Thus, the prior art matrices have been extremely limited in the temperatures at which the matrices could be constructed, observed, and preserved for later use. The result has been that the practical use of these low temperature inert gas matrices has been extremely limited; indeed, the only real use has been to provide a means to scientifically study the spectroscopy of the isolated component under these extreme temperature conditions.
Solid solutions of the prior art which may exist at room temperature include inclusion compounds, which typically comprise a solid material which is porous to a vapor component. The solid material and vapor component are miscible, and the vapor component continually enters and exits the solid material in an equilibrium situation which is determined, to a large extent, by the pressure of the vapor component outside of the solid material. Thus, in the prior art inclusion compounds, the vapor components are not trapped within the solid material in a fixed state, but rather move in and out of the solid material according to the principles of chemical equilibria.
In the prior art, thin layers of metal alloys have been vapor deposited at room or high temperatures, typically on a heated surface significantly above room temperature. Such high temperature deposition is often important in forming these metal alloy thin layers. For instance the high temperatures provide for good epitaxial growth and increased translation of the metal components within each other so as to enhance the desirable properties of the thin layers produced.
From the foregoing, it will be appreciated that it would be a significant advancement in the art if novel solid solutions of heretofore immiscible chemical components could be prepared and especially solid solutions which are stable at temperatures greater than 50K. It would be a further significant advancement in the art to provide a method for forming novel solid solutions from heretofore immiscible chemical components wherein the solid solutions are stable at room temperature, and often much higher temperatures, so as to allow the solid solutions to be used in a greater variety of applications. For example, it would be an advancement in the art to provide such solid solutions for isolating and preserving chemical components which are unstable in air, have bad odors, are toxic, are highly reactive, or are explosive in bulk. Such solid solutions and methods for forming these solid solutions are disclosed and claimed herein.